This invention relates to a valve manifold placed between a main flow line and a differential pressure transmitter to control the flow of high and low fluid pressures from the main flow line to the transmitter.
Normally, a flow restriction is placed in a main flow line for conveying a fluid and pressure taps are made on each side of the restriction for obtaining a high and low fluid pressure. Such a flow restriction may comprise an orifice plate, flow nozzle, or venturi tube, for example. The high and low pressures taken from opposed sides of the restriction in the main flow line are communicated to the transmitter for receiving the fluid pressure differential and transmitting the measured pressure differential by a suitable electronic signal or the like to a remote location, such as a control room, where the pressure differential may be monitored and/or recorded by an operator.
The differential pressure transmitter may be a direct reading instrument such as a manometer, or a differential pressure cell producing an output signal corresponding to the difference in pressures observed, the output signal being applied as the input to either a local or remote indicator or recorder registering either the pressure differential or a variable, such as a flow rate, which is a function of the pressure differential. However, this invention is particularly adaptable for use with a transmitter which transmits the differential pressure by an output signal to a remote location such as a control room where an operator may monitor the pressure differential in the flow line. This invention could also be used with differential pressure chart recorders.
Valve manifolds have been utilized heretofore to control the flow of fluid pressures between a differential pressure transmitter and a main flow line in which the fluid pressure differential is desired to be measured.
For example, the U.S. Pat. No. 3,450,157 dated June 17, 1969 and issued to John E. Hewson shows a valve manifold between a pipeline and a measuring instrument or transmitter with the manifold having a body and a pair of rotatable ball valves therein mounted on a stem which is actuated by a handle positioned outside the manifold body. Slots are provided in the ball valve members of Hewson so that both sides of a metering chamber are exposed to the high pressure for an instant prior to the rotation of the ball valve members to the fully open position, thereby to obtain increased meter accuracy and also to prevent damage to the metering device. FIG. 5 of Hewson shows the run position directing the high and low fluid pressures to the transmitter, and FIG. 6 shows the off position in which the high and low pressure ports from the measuring device or transmitter are vented to atmosphere. However, there is no showing of a separate calibration position for calibrating the manifold to a desired fluid pressure range.
U.S. Pat. No. 3,894,559 dated July 15, 1975 and issued to Leland Q. DePuy also shows a manifold adapted to be positioned between a process line or the like and a differential pressure sensing or reading instrument. The manifold of DePuy has a body with a pair of spaced ball valve members mounted on a stem for rotation, and positioned within an enlarged bore on the body which defines a fluid chamber between the stem and the bore surfaces. The ball valve members are rotatable between three settings: a first setting in a process mode, a second setting in a zero mode, and a third setting in a calibration mode. The stem is manually rotated for movement of the valve members among the three separate settings. In the process or run mode, the high and low passages of the valve members are aligned with the inlet and outlet ports of the manifold. In the calibration mode, the transmitter or measuring instrument is placed out of operating condition by having spherical surface portions of the valve members covering both the inlet and outlet ports within the valve to isolate the ports from each other. In the zero mode, high pressure from the inlet of the main flow line is communicated through the main bore space and to both the instrument high and low outlet ports, and thence to the pressure differential transmitter for applying a zero differential pressure for zero checking. It is noted that the calibration setting or mode blocks both inlet ports and both outlet ports to isolate the ports from each other. Again, there is no showing of a separate calibration position for calibrating the manifold to a predetermined fluid pressure range or to atmospheric pressure if desired.
U.S. Pat. No. 3,596,680 dated Aug. 3, 1971 issued to Donald L. Adams and is another example of a differential pressure device including a manifold utilizing two tapered plug valves which are movable between four basic positions: a normal operating or run position, a zero position, a calibration position, and a blowdown position. For calibrating the differential pressure transmitter to a predetermined differential pressure, a pair of cap screws must be manually removed from calibrating inlets, and calibrating pressure lines manually attached to such calibrating inlets thereby requiring a workman at the site of the manifold for calibration of the transmitter. Other known prior art is not believed to be any more pertinent than the above mentioned references.